1. Field of the Invention
This invention relates generally to a method of forming an intravascular device and more specifically for fabricating a catheter device.
2. Description of Related Art
Intravascular devices such as catheter assemblies are generally used for passing fluids between a device such as a syringe or a drip to or from body lumens such as veins or arteries, or other internal target sites. Such an assembly usually includes a hub, a catheter tube, and a needle. An eyelet ring is typically inserted into the catheter tube. The catheter tube, together with the eyelet ring, is then inserted into an opening in the nose of the hub and is secured to the hub by press fitting the eyelet ring within the nose of the hub. This hub and tube assembly is then mounted over a sharp needle which is in turn attached to a plastic hub. The sharp tip of the needle is used for piercing a body lumen so that access may be gained into the body lumen by the needle and subsequently the catheter. Once the catheter and the needle are located within the body lumen, the needle is removed and discarded while the catheter tube remains in the body lumen. A syringe or a tube of a drip is then attached to the hub so that fluids may be passed through the hub and the catheter between the drip or the syringe and the body lumen. The hub is typically made of materials that provide sufficient rigidity to securely attach drip lines thereto and the catheter tube is usually made of a material which is flexible and soft to minimize bodily injury.
Hubs used in catheter assemblies are generally made by using injection molding. However, over-the-needle catheter tubes are usually made by an extrusion process and cut into short pieces instead of a single injection molded piece for two reasons. First, it is generally considered impractical to use a core pin of the same length as the tube in a conventional core pin injection molding process. This is because the core pin is often bent or broken in a high speed manufacturing environment resulting in frequent down time. Second, it is also generally thought by those skilled in the art that the gas assisted injection molding process cannot be used because the length of the tube in relation to the thickness of the thin wall exceeds the generally accepted aspect ratio of greater than 200. The aspect ratio is the length of the cylinder or tube divided by the wall thickness of that cylinder or tube.
Although plastic needles have been manufactured using injection molding with gas assist manufacturing as shown in U.S. Pat. No. 5,620,639 issued to Stevens et al., a plastic needle is very different than a catheter. First, the geometry of a needle is quite different from that of an intravenous catheter. A needle requires the presence of a sharp point on the distal end of the needle to ease the penetration of the needle into the vascular system, whereas an over-the-needle catheter requires a bevel or taper at the distal end in order to provide a smooth entry of the catheter into the vascular system. The bevel must fit precisely over the needle to allow for the smooth entry of the catheter into the vascular system with the least trauma to the patient. Second, a needle requires the use of a high modulus material for the efficient penetration of the vascular system in contrast to catheters that require flexible and soft materials to minimize bodily injury. Materials with tensile modulii above 10,000 megapascals (MPa), such as liquid crystal polymers and fiber-filled polyamides, are generally suitable for the production of plastic needles whereas materials with tensile modulii of less than 300 MPa are suitable for catheters. Additionally, over-the-needle catheters must have flow rates of the fluids that are to be provided to the patient to conform with ISO International Standard 10555-5, whereas there is no such standard for needles. It is therefore desirable to use a material capable of forming a lengthy, soft and flexible tube for an intravascular device that includes a bevel at the distal end of the tube and a luer lock at the proximal end of a hub.
An apparatus and a method are disclosed for manufacturing an integral one-piece catheter having a tube and a hub by using a gas assisted injection molding process. The method comprises feeding molten material into a mold having a mold cavity. In one embodiment, the molten material is injected near or into the hub portion of the cavity. In another embodiment, the molten material is injected into the catheter tube portion of the mold. While the polymer is introduced into the cavity, a fluid such as a gas is then injected through an inlet of the mold into the material in the cavity forming a channel throughout the center of the injected material. This may also cause a portion of the molten polymer to be displaced by the gas into a spillover exit.
Another embodiment of the invention involves forming a first portion of an intravascular device using a first material in a first mold. Thereafter the first portion of the intravascular device is inserted into a second mold to form a second portion using a second material. The second mold is formed on or around the first mold. A fluid such as a gas is then injected through an inlet of the mold into the cavity forming a channel throughout the center of the tube cavity. This may result in a portion of the molten polymer to be displaced by the gas into a spillover exit area.
In yet another embodiment of the invention, a first portion of the mold is injected with a first material, and a second portion of the cavity is injected with a second material at or around the same time that the first material is injected into the first portion of the cavity. A fluid such as a gas is injected through an inlet of the mold into the cavity. This causes a portion of the molten polymer to be displaced by the gas to conform to the mold with excess material displaced into the spillover exit area. In another embodiment of the invention, injected polymer is precisely measured to prevent spillover of excess molten polymer. In both of the previous cases, a hollow channel is formed throughout the center of the tube cavity.
Additional features, embodiments, and benefits will be evident in view of the figures and detailed description presented herein.